Eighteen-month caries incidence among older adult residents of fluoridated and nonfluoridated communities was compared. Rates for both coronal and root caries were consistently lower among long-term residents of the fluoridated communities than among life-long residents of nonfluoridated communities. Coronal caries incidence was significantly lower for people who had resided in fluoridated communities for more than 30 years (1.95 vs 1.33 surfaces). Root caries incidence was significantly less among residents for more than 40 years (0.56 vs 1.11 surfaces). Fluoridation appeared to be beneficial for the older adults examined, even though the exposure to fluoridated water began in adulthood.